Atomic layer etching is a cyclic dry etching process used in the semiconductor manufacturing industry to remove one layer of the material to be etched per cycle.
Many etchants have been disclosed for use in continuous (i.e., non-cyclic) etch process. See, e.g., US2015/011093 and US2015/017810.
Many initial processes use a plasma etch gas cycle followed by a plasma inert gas cycle. For example, the December 2013 issue of Solid State Technology magazine discusses an atomic layer etching process of a silicon layer using chlorine (Cl2) and Argon (Ar). U.S. Pat. No. 4,756,794 discloses an atomic layer etching method to remove diamond by NO2 followed by ion bombardment. Agarwal and Kushner presented the computer simulated results of atomic layer etching of a Si layer using a cycle of Cl2/Ar followed by Ar alone and atomic layer etching of a SiO2 layer using a cycle of c-C4F8/Ar followed by Ar alone (Plasma Atomic Layer Etching Using Conventional Plasma Equipment at the 53rd AVS Symposium in November 2006). CN103117216 discloses an atomic layer etching method to remove an oxide or gate dielectric layer using a fluorocarbon gas (CxFy, specifically CF4) mixed with an inert gas (Ar) followed by Ar. US2014/206192 discloses an atomic layer etching method to remove graphene using O-based (such as CO2, O2, NO2), F-based (such as C4F8, CF4, or CHF3), H-based (such as H2, NH3, or SiH4) gas plasmas, or combinations thereof, followed by an energy source (such as neutral beam, ionic beam, heat energy, plasma, laser, or combinations thereof). The neutral beam may contain He, Ar, N2, Ne or Xe. KR20110098355, KR101465338, and KR101466487 disclose atomic layer etching methods using BCl3 followed by irradiation by Ar or Ne ion beam or neutral beam to remove single layers of HfO2/ZrO2/Ta2O5; Al2O3, or BeO; respectively. U.S. Pat. No. 8,617,411 discloses an atomic layer etching method using Cl2, HCl, CHF3, CH2F2, CH3F, H2, BCl3, SiCl4, Br2, HBr, NF3, CF4, SF6, O2, SO2, COS, etc., followed by an inert gas (Ar, He, Kr, Ne, Xe, etc).
However, as these methods do not always remove the layer in a satisfactory manner, additional variations of atomic layer etching have been developed. For example, Lee and George disclose atomic layer etching of Al2O3 using sequential, self-limiting thermal reactions with Sn(acac)2 and HF (ACS Nano, 2015, 9 (2) pp. 2061-2070). JP58098929 to Seiko Epson Corp. discloses an atomic layer etching method to remove SiO2 from a Si substrate by HF followed by I2. U.S. Pat. No. 8,633,115 disclosed an atomic layer etching process to remove SiO2 by introducing H2O or NH3 followed by HF and a temperature change. U.S. Pat. No. 8,124,505 discloses a two stage plasma technique using oxygen to oxidize the surface of the aluminum gallium nitride barrier layer followed by using BCl3 to remove the oxidized layer.
A need remains for more precise dry processes to selectively remove layers without damaging the surrounding materials or leaving significant residue on the substrate.